1. Field of the Invention
The present invention relates to an image forming apparatus for preventing the delay in transmission of video data to an engine, and to a video data transmitting method therefor.
2. Description of the Related Art
An image forming apparatus such as a printer or a copier forms an image corresponding to received print data on a sheet of paper. A printer receives print data from a computer connected to the printer through a communications interface while the copier receives print data from a scanner scanning an object to be copied.
FIG. 1 is a view showing the structure of a conventional image forming apparatus. Referring to the drawing, the image forming apparatus includes a central processing unit (CPU) 11, a main frame buffer memory 12, a direct memory access (DMA) controller 13, a video data output controller 14, a video sync signal controller 15, and an engine 16.
The CPU 11 converts print data received from the outside to video data suitable for driving the engine 16 and stores the converted video data in the main frame buffer memory 12.
The engine 16 is configured to print and output an image corresponding to the received video data in a sheet of paper. To enable the engine 16 to begin an image print task using a sheet of paper, each of parts the constituting the engine 16 should be in a ready mode to perform the print task. When receiving a print command from the CPU 11, the engine 16 requires has each part to be ready to perform the print task. That is, a rotary polygonal mirror or a scan disk (a disk where a holographic pattern for deflecting input light is formed), which are deflection devices in a laser scanning unit, is rotated to set speeds required for performing the print task, a transfer device is heated to a set temperature, or each part is checked whether there is any problem in performing the print task. When the preparation of performing the print task is completed, the engine 16 outputs a print start signal for indicating that it is possible to start the print task to the video sync signal controller 15.
The DMA controller 13 controls the main frame buffer memory 12 such that the video data stored in the main frame buffer memory 12 can be output to the video data output controller 14 when a print start signal is output from the video sync signal controller 15 from the engine 16.
The video data output controller 14 temporarily stores the video data received from the main frame buffer memory 12 and outputs the video data to the engine 16 by being controlled by the video sync signal controller 15.
The video sync signal controller 15 controls the operation of the DMA controller 13 and the time when the video data is output from the video data output controller 14 according to a video data output control signal output from the engine 16. The video data output control signal output from the engine 16 includes a print start signal, a print stop signal, and a video clock sync signal. The print stop signal is generated from the engine 16 when the video data corresponding to a single page and/or file is completely written to a photoreceptor medium. The video clock sync signal is output from a video clock generator (not shown) provided in the engine 16 for recording of the video data on the photoreceptor medium according to a position a pixel.
The video data output controller 14 outputs the video data to the engine 16 by synchronizing the same with the video clock signal output from the video sync signal controller 15.
In a method for transmitting video data from the main buffer memory 12 to the video data output controller 14 in the conventional image forming apparatus, as shown in FIG. 2, when a print start signal is output from the video sync controller 15, a main frame buffer memory access controller 13a of the DMA controller 13 controls output of video data from the main frame buffer memory 12 so that the video data stored in the main frame buffer memory 12 is transmitted to the video data output controller 14. When the video data transmitted from the main frame buffer memory 14 completely fills an inner memory, the video data output controller 14 outputs a FF (full flag) signal indicating that the data is full. When the FF signal is input, the main frame buffer memory access controller 13a stops transmission of the video data from the main frame buffer memory 12 to the video data output controller 14. Also, when the stored video data is all output to the engine 16 and no video data is left, the video data output controller 14 outputs an empty signal to the main frame buffer memory access controller 13a. Then, the main frame buffer memory access controller 13a controls again the transmission of the video data until the video data output controller 14 is completely filled with the video data stored in the main frame buffer memory 12.
In the above conventional video data transmission method, a delay in time between the point when the video data is received from the main frame buffer memory 12 and the point when the empty signal is output from the video data output controller 14 is generated. As a result, when a high speed printing is performed, the time delay until the video data is received after the video data in the video data output controller 14 is emptied, lowers the entire print time.
To solve the above problem, it is an objective of the present invention to provide an image forming apparatus which can present a time delay in the transmission of video data to an engine and a video data transmitting method therefor.
Accordingly, to achieve the above objective, there is provided an image forming apparatus which comprises an engine for forming an image corresponding to received video data on a sheet of paper, a main frame buffer memory, an auxiliary frame buffer memory for outputting stored video data along a data transmission path to the engine according to a video clock sync signal, and a first signal when a lower level correspondingly set to at least some amount of the stored video data is reached, and a second signal when the stored data reaches a set upper level. The apparatus further comprises a central processing unit for converting print data received externally to video data suitable for driving of the engine and storing the converted video data in the main frame buffer memory and a direct memory access controller for controlling the main frame buffer memory so that video data stored in the main frame buffer memory is transmitted to the auxiliary frame buffer memory until the second signal is output when a print start signal is input, at an initial stage, and the video data stored in the main frame buffer memory is transmitted to the auxiliary frame buffer memory as much as a set data transmission amount whenever the first signal is input, at a subsequent stage after the initial stage. There is also provided a video sync signal controller for controlling operation and interruption of the direct memory access controller according to a video data output control signal output from the engine and outputting the video clock sync signal.
It is preferred in the present invention that the auxiliary frame buffer memory outputs a third signal when a medium level set between the upper level and the lower level to a predetermined amount of the stored video data is reached, and the direct memory access controller controls the main frame buffer memory so that the video data stored in the main frame buffer memory is transmitted to the auxiliary frame buffer memory until the third signal is output, whenever the first signal is output at the subsequent stage.
Also, it is preferred in the present invention that the direct memory access controller controls the main frame buffer memory so that the video data stored in the main frame buffer memory is transmitted to the auxiliary frame buffer memory until the second signal is output, whenever the first signal is output at the subsequent stage.
Also, it is preferred in the present invention that the print start signal is generated from the engine and output to the direct memory access controller through the video sync signal controller, and that a print stop signal is generated from the engine and output to the direct memory access controller through the video sync signal controller, and the direct memory access controls the main frame buffer memory, when the print stop signal is received, so that the transmission of video data from the main frame buffer memory to the auxiliary frame buffer memory is interrupted.
Also, it is preferred in the present invention that the image forming apparatus further comprises a video data output controller for temporarily storing video data output from the auxiliary frame buffer memory and outputting the video data to the engine according to the video clock sync signal.
To achieve another aspect of the present invention, there is provided a method of transmitting video data of an image forming apparatus including an engine for forming an image corresponding to received video data on a sheet of paper, a main frame buffer memory, and an auxiliary frame buffer memory for outputting stored video data along a data transmission path to the engine according to a video clock sync signal and outputting the information of the amount of video data stored. The method further comprises a central processing unit for converting print data received externally to video data suitable for driving of the engine and storing the converted video data in the main frame buffer memory, a direct memory access controller for controlling the main frame buffer memory so that video data stored in the main frame buffer memory is transmitted to the auxiliary frame buffer memory by using the information of the amount of video data stored from the auxiliary frame buffer memory, and a video sync signal controller for controlling operation and interruption of the direct memory access controller according to a video data output control signal output from the engine and outputting the video clock sync signal. The method comprising the steps of (A) determining whether a print start signal is input, (B) if the print start signal is determined to be input, transmitting video data from the main frame buffer memory to the auxiliary frame buffer memory, (C) determining whether the amount of video data stored in the auxiliary frame buffer memory reaches a set upper level, (D) if it is determined that the set upper level is reached, interrupting the transmission of video data from the main frame buffer memory to the auxiliary frame buffer memory, (E) determining whether the amount of video data stored in the auxiliary frame buffer memory reaches a lower level which is set to a state that some amount of video data is left as the video data is transmitted to the engine, and (F) if it is determined that the set lower level is reached, transmitting a set amount of video data from the main frame buffer memory to the auxiliary frame buffer memory.
Also, it is preferred in the present invention that, if it is determined that the amount of video data stored in the auxiliary frame buffer memory reached the set lower level, transmitting the video data from the main frame buffer memory to the auxiliary frame buffer memory until the amount of the video data stored in the auxiliary frame buffer memory reaches a medium level set between the upper level and the lower level as a predetermined data amount is reached.
Also, it is preferred in the present invention that the method further comprises a step (G) of repeating the steps (E) and (F) until a print stop signal is input.